Receivers for television signals

ABSTRACT

A television signals receiver for receives and stores television signals encoded at a variable data rate. Time information is generated based on the time of receipt of the signals that defines the duration of the television signals when output in decompressed form at a substantially constant data rate. The received signals are then written to a file on a hard disk ( 13 ) in received order together with the time information. The time information of signals stored in the file is monitored and old signals are deleted from the file such that the file stores signals corresponding to a predetermined period of time.

This invention relates to methods and apparatus for recording televisionsignals for subsequent playback and, more specifically, to improvementsin the storage of data representing television signals and such like andimprovements in the control of recording and playback.

In recent years there has been a move towards broadcasting televisionsignals in digital form. Suitable receivers/recorders (also known as‘set top boxes’, but generally referred to herein as ‘receivers’) havebeen developed to take advantage of the digital format to allow theviewer, among other things, to record one television programme whilewatching another. An example of such a receiver is described in ourInternational patent application published as WO-A-01/11865, theteachings of which are incorporated in this document by reference.

The receiver described in that International patent application isarranged to receive signals representing television programmes andtelevision programme schedule data and has a recorder comprising a “harddisk” for recording received television programmes. The receiverconstantly receives updated programme schedule data in a dedicatedprogramme schedule data channel and is arranged to output the programmeschedule data for display on a television screen. A user can use thedisplayed programme schedule data to select programmes for recordal.

The receiver is also arranged to receive additional programme scheduleinformation included in each received television channel, whichinformation is used to control the hard disk to record user-selectedpre-programmed television programmes. The hard disk is operable torecord simultaneously two different television programmes received indifferent channels. Also, the receiver is operable to replay a currentlybroadcast programme offset in time. The time offset can be overcome byplaying back the part of the programme inside the time offset at anincreased frame rate. Furthermore, the receiver is arranged to receivetransition signals indicating transitions between parts of programmes.Transitions might be between different items in a magazine formatprogramme, for example a sports magazine programme or music videoprogramme. The recorder is operable to use these transition signals, forexample, to skip between parts of recorded programmes replayed from thehard disk.

Some receivers include a facility for recording a programme while it isbeing viewed to enable “instant” playback of a portion of the programmewhile it is still being broadcast. Instant playback recording mightbegin automatically when the viewer first switches to a channel andmight continue until such time as the viewer switches from the channelor until an allotted memory space is full up. Recording can be automaticas it can be done without any intervention by the viewer.

Instant playback recording may be implemented by recording a programmeas data in a so-called cyclic file, such as described in EP1185095. Acyclic file is generally a data file of fixed size, e.g. a certainnumber of bytes such as 2 gigabytes. Data may be recorded in a cyclicfile as it is received until the file is full of data. At that point therecording continues from the beginning of the file, writing over thedata previously recorded in the file. Thus, the cyclic file alwayscontains the most recent viewed portion of a programme as far as thesize of the cyclic file allows.

The size of a cyclic file used by a receiver is typically selected suchthat it can store a length of program likely to be useful to a viewerwhilst bearing cost considerations in mind. As memory costs have fallenand sizes of, for example, hard disk memories have increased, the amountof time that can be recorded in cyclic files has increased. At present,a cyclic file may typically be expected to store received video data ofapproximately 30 minutes to one hour in length, thus giving the viewerthe option of instant playback of any portion of a programme from up toone hour previously.

Compression techniques are used to compress digital television databefore it is transmitted. A frame of video showing, say, a crowd sceneis generally much more complex than a frame of video showing, say, acommentator in front of a plain background and thus will be moredifficult to compress without introducing unwanted artefacts. Similarly,video including significant changes between frames, such as video offast moving scenes, is generally more complex than slower changingvideo. Less compression can therefore be applied to some video, such asthe crowd scene, than to other video, such as the commentator, in orderto maintain the same level of perceived quality. To try to maintain thesame level of perceived quality, but at the same time compress the videodata as much as possible, the rate at which video data is transmittedcan therefore be varied depending on content. This is known as VariableBit Rate (VBR) encoding. For example, during transmission of the crowdscene a data rate of 6 megabits per second may be used, while duringtransmission of the commentator, only 3 megabits per second may be used.It is therefore not possible to know in advance how much disk space willbe required to store data for 30 minutes (say) of a programme when VBRencoding is used.

Furthermore, it is common for broadcasters to vary the bandwidthallocated to a channel in order to accommodate demands on theirnetworks. For example, a particular uplink to a satellite of a satellitenetwork may have a fixed bandwidth, i.e. data rate, of (say) 20 megabitsper second available to transmit data to a given satellite. Thisbandwidth may be divided between the channels broadcast via thesatellite, generally such that the full available bandwidth isexploited, i.e. such that there is little or no spare bandwidth.However, the bandwidth required by each channel may vary from time totime. Furthermore, the number of channels to be transmitted on theuplink may change from time to time, e.g. during the course of a day.The bandwidth allocated to a channel and hence the data rate at whichparticular programmes are received at a receiver may therefore vary.Again, it is therefore very difficult to determine, in advance, the sizeof a cyclic file that will be required to store 30 minutes (say) of agiven programme.

To ensure that a user always has at least 30 minutes (say) of content onthe disk, cyclic files have therefore been made as large as may benecessary to cover the worst case, e.g. to make the file large enough tostore 30 minutes (say) of video data transmitted with the lowestcompression, i.e. at the highest data rate. This is wasteful of diskspace. Having to dedicate memory for the greatest possible memoryrequirement for the cyclic file also limits the user's choice. It mayalso be unpredictable for a user, as the user is not certain whether thecyclic file contains 30 minutes (say) of a programme, more or less.

According to the present invention, there is therefore provided a methodof storing data comprising: receiving data at a variable data rate thatrepresents an information stream; storing the data; determining theexpected duration of the information stream represented by the storeddata should the information stream be reproduced as intended; anddeleting the oldest stored data when the determined duration reaches agiven period such that the determined duration does not exceed the givenperiod.

Also according to the present invention there is provided an apparatusfor storing data comprising: a receiver for receiving data at a variabledata rate that represents an information stream; a storage device forstoring the data; and a processor for determining the expected durationof the information stream represented by the stored data should theinformation stream be reproduced as intended; wherein the storage devicedeletes the oldest stored data when the determined duration is greaterthan a given period such the determined duration does not exceed thegiven period.

Thus, the amount of stored data is determined by the duration of theinformation the data represents, e.g. by the length of stored video orstored television signals when viewed as normal. This has the advantageof being able to provide a buffer, e.g. for a television signal, thathas a maximum capacity defined by the duration of the information it isintended to contain, e.g. a television programme of say 30 minutes,rather than the amount of data that can be stored in the buffer, e.g. 2gigabytes. This is far more predictable for a user as the user can bemore certain of the length of the stored information stream. Providedenough data has been received and stored to reach the given period, thestorage device, memory or buffer will always store data representingsubstantially the given period of the information stream.

The information stream is typically a continuous signal intended to bereproduced at a known or predictable rate. For example, the informationstream may be a video steam or an audio stream, such as a television orradio signal. In particular it may be a satellite television broadcastusing, for example, the Digital Video Broadcast/Moving Picture ExpertsGroup 2 (DVB/MPEG 2) standard. Television signals are normallyreproduced at a known number of frames per second. In particular, theinformation stream may therefore be intended to be reproduced at asubstantially constant rate, e.g. a constant frame rate.

The expected duration of the stream of information represented by thedata can be determined in a variety of ways. For example, the data maycontain headers or markers providing timing information for reproductionof the information that can be read to determine the expected duration.The so-called “I-frames” of the MPEG standard may be produced at knownintervals and therefore provide such markers. Alternatively, knowledgeof the amount of data received, along with it's compression rate whereappropriate, may be used to determine expected duration. However, it isparticularly preferred that the expected duration of the stream ofinformation represented by the data is determined as the length of theperiod during which the stored data was received. This exploits theknowledge that for certain signals, such as DVB/MPEG 2 broadcasts, datarepresenting information to be displayed in a particular time period istransmitted over a time period of the substantially same length(although the amount of data in respective periods may vary, e.g.according to the amount of compression applied). In other words, forcertain signals, the data received in a one second interval relates toinformation to be reproduced in a one second interval so that loggingthe time it takes to receive the data logs the expected duration of theinformation stream when it is reproduced as intended. The preferredmethod is particularly straightforward and convenient as it requiresminimum processing to implement.

The given period is typically a default period, for example stored insoftware used to implement the method or apparatus. However, it isbeneficial for a user to be able to vary the given period. This mayallow a user to choose how memory resources are allocated. The apparatusmight therefore comprise means, such as a controller, by which the usermay vary the given period. Typically, the given period might have adefault of 30 minutes and be varied by the user to one of 0 minutes(i.e. turned off), 5 minutes, 15 minutes, 30 minutes or 1 hour, or anyother convenient period subject to the maximum memory space available.

The storage device may be any of a variety of suitable memory units,such as computer RAM (Random Access Memory), CD-RW (CompactDisc—Re-Writable) drive, DVD-RW (Digital Video/Versatile DiscRe-Writable) drive or Flash memory.

However, it is particularly preferred that the storage device is a harddisk drive, such as a conventional computer hard disk. Hard disks havelarge capacity, are robust and have fast read and write rates. They aretherefore suited to this invention, particularly when video data isstored, which has a relatively high data rate.

Typically, the received data is therefore stored in a file in a memory.In other words, the storage device stores the data as a file in amemory. The remainder of the memory may be used by other applications orto store other data. To facilitate this, the size of the file may bedynamically adapted to equal the amount of stored data. Whilst theduration of the stream of information represented by the stored data mayremain substantially constant, the size of the file in which the data isstored varies according to the amount of stored data, which in turndepends on the rate at which data is received.

As it was always necessary for the cyclic files of the prior art to belarge enough to cover the worst case, i.e. to store (say) 30 minutes ofdata received at the maximum data rate, these cyclic files took up alarge amount of memory space. However, memory space can be allocated tothe stored data of the invention dynamically, as the amount of storeddata is monitored according to the duration of the information itrepresents. Thus, during periods of low received data rate, the file inwhich the data is stored can be smaller than during periods of highreceived data rate. Memory space can therefore be allocated to the fileand to other applications or other stored data more efficiently. Inother words, the need in the prior art to reserve memory space which issurplus to requirements during periods of low received data rate isobviated by the invention.

Other applications or stored data might include recordal of entireprogrammes, or a particular broadcast, between fixed start and end timesas facilitated by Personal Video Recorders (PVRs) and such like. Datafiles for such recordings may be regarded as ‘linear’ in that there isnot usually any deletion of the start of the file that limits the sizeof the file, such as the prior art cycling back to overwrite earlierdata with new data Rather, linear files are usually of indeterminatelength.

An example of how broadcast data is processed for storage in linearfiles on a hard disk is described in International patent applicationpublished as WO-A-01/35669. Broadcast data is transmitted in scrambledform to protect the content from unauthorised viewing. The publishedpatent document describes an apparatus and method for processingscrambled data streams, in which the scrambled data is recorded in itsscrambled state and is only descrambled at the time of playback.

When a receiver provides instant playback recording of receivedtelevision programmes as discussed above, it may be desirable to allow auser to save the instant playback recording. A user can then, forexample, choose to save an entire programme after it has started bysaving the instant playback recording along with the remainder of theprogramme. However, recordings of entire programmes are usually made inlinear files and the instant playback recording is usually made in acyclic file. The cyclic files and the linear files of the prior art areincompatible with one another. It is not therefore a simple task toconvert between a cyclic file structure and a linear file structure. Forexample, when a cyclic file is stored on a hard disk, a given space onthe hard disk, of the predetermined size, is generally permanentlyallocated to the cyclic file. This can reduce choice and usability forthe user by committing memory space that could be allocated to otheruses. Furthermore, if, at some stage, it is desirable to store in alinear file the data stored in such a cyclic file, it is necessary tocopy the data from the cyclic file into a new linear file. Thisoperation is generally inefficient, for example, in use of processingand memory resources, and undesirable.

A preferred feature of the invention is therefore that the data isstored as a data file and that the oldest stored data is deleted bymoving the start of the data file to data representing information laterin the stream of information. The data can then be stored in effectivelythe same way as data is stored in a linear file, except that the startof the file can be moved to delete the earliest or oldest data from thefile and limit the size of the file. Should it be desired to convert thefile to a linear file, movement of the start of the file is simplystopped. This is clearly more efficient than the prior art.

The applicants consider this to be new in itself and, according toanother aspect of the present invention there is therefore provided amethod of storing data, comprising storing a data stream as a data filein a memory such that it does not exceed a specified size by deletingthe oldest data from the data file whilst storing new data at the end ofthe data file, wherein the oldest data is deleted by moving the start ofthe data file to later in the stored data stream.

According to another aspect of the present invention there is providedan apparatus for storing data, comprising means for storing a datastream as a data file in a memory and a file manager for ensuring thatthe data file does not exceed a specified size by deleting the oldestdata from the data file whilst new data is stored at the end of the datafile, wherein the file manager deletes the oldest data by moving thestart of the data file to later in the file.

Unlike the prior art, the oldest data is not simply overwritten. Rathernew data is added to the end of the data file as if it were a linearfile. The start of the data file is redefined to maintain the size ofthe file and as the start of the file is moved, the memory used by theoldest data is returned to the memory for general use. Thus, at anyparticular time, the data file actually resembles a linear file, and cantherefore be converted to such simply by stopping the deletion process.Thus, conversion of the file from a “buffer” to a linear file isstraightforward.

As mentioned above, the memory is typically a hard disk or such like.More generally, the memory may therefore be formatted as plural storagesectors and the data file may occupy a series of the storage sectors.The start of the data file may be identified as at a particular storagesector The start of the data file may be moved by identifying anotherparticular storage sector later in the series of storage sectors suchthat the preceding storage sectors in the series are removed from thedata file. This implementation is particularly convenient.

Overall, according to another aspect of the invention there is provideda method of storing data, the method comprising: receiving data in adata stream comprising compressed video data delivered at a variabledata rate; generating time information based on the time of receipt ofthe data and relating to the duration of the data when output indecompressed form at a substantially constant data rate; writing thereceived data to a file in a store in received order together with thetime information; monitoring the time information of data written to thefile; and deleting data from the file from the file when the totalamount of data in the file corresponds to a period of time greater thana predetermined period so that at any instant in time the amount of datain the file is of a duration equal to or not substantially greater thanthe predetermined period.

According to another aspect of the present invention, there is providedan apparatus for storing data, the apparatus comprising: means forreceiving data in a data stream comprising compressed video datadelivered at a variable data rate; means for generating time informationbased on the time of receipt of the data and relating to the duration ofthe data when output in decompressed form at a substantially constantdata rate; means for writing the received data to a file in a store inreceived order together with the time information; mean for monitoringthe time information written to the file; and means for deleting datafrom the file when the total amount of data in the file corresponds to aperiod of time greater than a predetermined period so that at anyinstant in time the amount of data in the file is of a duration equal toor not substantially greater than the predetermined period.

According to another aspect of the invention there is provided a methodof recording data representing programmes for subsequent playback of theprogrammes, the method comprising: storing one set of received data forone programme in a store while simultaneously outputting the same datafor display of the programme represented thereby, the one set ofreceived data being stored in accordance with the above method; andrecording another set of received data for another programme in thestore.

The invention also provides an apparatus for recording data representingprogrammes for subsequent playback of the programmes, the apparatuscomprising: means for storing one set of received data for one programmein a store while simultaneously outputting the same data for display ofthe programme represented thereby, the one set of received data beingstored by the above apparatus; and means for recording another set ofreceived data for another programme in the store.

The invention also provides a method of recording television programmes,the method comprising storing times that programmes are to be recordedand revising the stored times if there is a overlap in the time that twoor more programmes are to be recorded to give priority to the programmehaving programme type with higher priority on a stored programme typepriority list.

The invention also provides an apparatus for recording televisionprogrammes, the apparatus comprising means for storing times thatprogrammes are to be recorded and means for revising the stored times ifthere is a overlap in the time that two or more programmes are to berecorded to give priority to the programme having programme type withhigher priority on a stored programme type priority list.

The invention also provides a method of making recordings of pluralprogrammes, the method comprising: generating a priority listidentifying types of programmes to be recorded and their relativepriorities; storing timing information relating to one or moreprogrammes to be recorded together with information identifying the typeof programme to be recorded; comparing entries on the priority list withthe stored timing and type information for each programme to berecorded; and revising the stored timing information in the event of aconflict between timing information for two or more programmes to berecorded, depending on the relative priorities of the conflictingprogrammes.

The invention also provides an apparatus for making recordings of pluralprogrammes, the apparatus comprising: means for generating a prioritylist identifying types of programmes to be recorded and their relativepriorities; means for storing timing information relating to one or moreprogrammes to be recorded together with information identifying the typeof programme to be recorded; means for comparing entries on the prioritylist with the stored timing and type information for each programme tobe recorded; and means for revising the stored timing information in theevent of a conflict between timing information for two or moreprogrammes to be recorded, depending on the relative priorities of theconflicting programmes.

The invention further provides a method of controlling a recorder torecord programmes, the method comprising: storing a priority listidentifying types of programmes to be recorded and their relativepriorities; storing timing information relating to one or moreprogrammes to be recorded together with information identifying the typeof programme to be recorded; receiving a data stream including datarepresenting programme content, programme identity data and dataidentifying the broadcast times of programmes; comparing the storedtiming information with the received data identifying the broadcasttimes of programmes; adjusting the stored timing information in theevent of a change as determined from the received data identifying thebroadcast times of programmes; comparing entries on the priority listwith the stored timing and type information for each programme to berecorded; and revising the stored timing information in the event of aconflict between timing information for two or more programmes to berecorded, depending on the relative priorities of the conflictingprogrammes.

The invention further provides an apparatus for controlling a recorderto record programmes, the apparatus comprising: means for storing apriority list identifying types of programmes to be recorded and theirrelative priorities; means for storing timing information relating toone or more programmes to be recorded together with informationidentifying the type of programme to be recorded; means for receiving adata stream including data representing programme content, programmeidentity data and data identifying the broadcast times of programmes;means for comparing the stored timing information with the received dataidentifying the broadcast times of programmes; means for adjusting thestored timing information in the event of a change as determined fromthe received data identifying the broadcast times of programmes; meansfor comparing entries on the priority list with the stored timing andtype information for each programme to be recorded; and means forrevising the stored timing information in the event of a conflictbetween timing information for two or more programmes to be recorded,depending on the relative priorities of the conflicting programmes.

Examples of the invention are now described with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic functional block diagram of a television receiver;

FIG. 2 is a schematic functional block diagram of a hard disk of thetelevision receiver of FIG. 1;

FIG. 3 is a schematic representation of a first recording timeline;

FIG. 4 is a schematic representation of a second recording timeline;

FIG. 5 is a schematic representation of a third recording timeline;

FIG. 6 is a schematic representation of a fourth recording timeline;

FIG. 7 is a schematic representation of a first conflict screen;

FIG. 8 is a schematic representation of a second conflict screen;

FIG. 9 is a schematic representation of a third conflict screen;

FIG. 10 is a schematic representation of a fourth conflict screen; and

FIG. 11 is a schematic representation of a fifth conflict screen.

FIG. 1 of the accompanying drawings shows a “set top box” or receiver 3for receiving television signals from a satellite television broadcastnetwork. In this example, received signals are input to first and secondtuners 10 a and 10 b but any plural number of tuners may be used in thereceiver 3. The tuners 10 a and 10 b are tuneable into the same ordifferent channels of the satellite television broadcast network forsimultaneous reception of the same or different television programmes.Signals from the first and second tuners 10 a and 10 b are passed to aQuadrature Phase Shift Key (QPSK) demodulator 11. Demodulated signalsare error-corrected by way of a forward error corrector circuit 12. Thereceiver 3 has a hard disk 13 which receives from the forward errorcorrector circuit 12 compressed video and audio data representingreceived television programmes for recording and subsequent playback, asdescribed in greater detail below.

The received signals comprise digitally encoded data. In this example,the data is compressed using the Digital Video Broadcast/Moving PicturesExpert Group 2 (DVB/MPEG 2) standard which permits both programme dataand additional data (for example interactive service data) to betransmitted in a single channel. DVB/MPEG 2 enables high compressionratios to be achieved. The hard disk 13 receives and stores compresseddata. The data is decompressed only after retrieval from the hard disk13.

Satellite (and indeed cable) programmes are usually scrambled to preventunauthorised access by non-authorised subscribers. The receiver 3therefore has a conditional access control circuit 14 which co-operateswith a smart card 14 a to determine whether the viewer has subscribed toa particular channel and is therefore authorised to access the channel.Parental control over channel access is also provided, at least in part,by the access control circuit 14. The receiver 3 further comprises adescrambling circuit 15 which is controlled by the access controlcircuit 14 to enable the descrambling of the signal by authorisedsubscribers.

Descrambled data is supplied to a transport/demultiplexer 16 whichseparates the data into video data, audio data, user services data,programme scheduling data, etc. for distribution to various locationswithin the receiver 3. The receiver 3 also comprises a videodecompression and processing circuit 18 utilizing a dedicated videoRandom Access Memory (RAM) 17, and an audio decompression and processingcircuit 19, operating according to the MPEG 2 standard, for example. Thevideo and audio decompression and processing circuits 18 and 19 receivedemultiplexed signals directly from the transport/demultiplexer 16, orfrom the hard disk 13. Decompressed video signals are input to aSyndicat des Constructions d'Appareits Radiorecepteurs et Television(SCART) interface 20 for direct input to the television (TV) 2 and to aPhase Alternation Line (PAL) encoder 21 where they are encoded into thePAL format for modulation by a Ultra High Frequency (UHF) modulator 22for output to the UHF input of the TV 2 if so desired.

The receiver 3 is controlled by a processor 23 which communicates withthe various units of the receiver via a bus 24. The processor 23 hasassociated with it Read Only Memory (ROM) 25 (optionally including aCompact Disc—Read Only Memory (CD-ROM) drive 25 a), Random Access Memory(RAM 26) and a flash (non-volatile and writable) memory 27.

The processor 23 controls operation of the receiver 3 by tuning thetuners 10 a and 10 b to receive signals for the desired channels bycontrolling the demultiplexing, descrambling and decompression so thatthe desired programme and/or interactive service data is displayed onthe screen of the TV 2, and by controlling the hard disk 13 to recorddesired television programmes or to play back previously recordedtelevision programmes. Viewer selection of desired programmes andcustomer services is controlled by viewer manipulation of a remotecontrol unit 28, which in response to such viewer manipulation transmitscontrol signals to a receiver 29 for input to the processor 23. Theremote control unit 28 also allows the viewer to control of theoperation of the hard disk 13 to record television programmes, to playback recorded television programmes and to program the recording oftelevision programmes, etc.

The receiver 3 further comprises a high-speed data interface 30 and aRecommended Standard 232 (RS232) interface 31 providing a serial link.The high-speed data interface 30 and the RS232 interface 31 may beconnected to a Personal Computer (PC) and/or a games console and/orother digital equipment (not shown). The high speed data interface 30enables the receiver 3 to be connected to other devices (not shown), forexample to enable reception of services transmitted via other media suchas broadband cable, external storage media or digital terrestrialbroadcast. The receiver 3 further comprises a modem interface 32 forconnecting a telephone network.

Operation of the receiver 3 is controlled by software that makes theprocessor 23 responsive to control signals from the remote control unit28, additional data in the received signals and/or data stored in thememory units 25 to 27. Interaction between hardware and software in thereceiver 3 is described in detail in our international patentapplication published as WO-A-01/11865. Operation of the receiver 3 inreceiving and decoding data representing television programmes and datadefining scheduling and other information related to the programmes isdescribed in detail in our international patent application published asWO 96/37996. Operation of the receiver 3 in providing interactiveservices is described in our international patent application publishedas WO 97/23997.

Within the Digital Video Broadcasting (DVB) standard for digitaltelevision broadcast there exists a standard for the transmission ofschedule information such that it can be decoded and presented correctlyto subscribers in the form of an Electronic Programme Guide (EPG). ThisDVB standard is known generally as the SI standard and can be found inthe specification: ETS 300 468, ETSI Digital Broadcasting Systems forTelevision, Sound and Data Services; Specification for ServiceInformation (SI) in Digital Video Broadcasting (DVB) Systems 2ndedition. Guidelines for using the specification are given in ETSI ETR211—DVB SI Guidelines. The receiver 3 is designed to support the SIspecification.

In addition to operating data for use in controlling access to channels,additional data in a channel can include brief programme schedule datarepresentative of so-called event information tables (EITs) defining thescheduling of programmes in each channel. The programme schedule data isused by the receiver 3 to control the operation of the hard disk 13.When the receiver 3 is programmed to record a selected televisionprogramme, the receiver 3 operates the hard disk 13 to start and to stopthe recording in accordance with the programme schedule data whichcomprises the start and the end time of the selected televisionprogramme. Since the programme schedule data is updated regularly, therecording is started and stopped in accordance with the updatedprogramme schedule, thus guaranteeing that a selected televisionprogramme is actually recorded even in case of a change of programmeschedule, because such change is reflected in the programme scheduledata in each channel.

The programme schedule data may be stored in the RAM 26 and, oncestored, the scheduling information is available effectivelyinstantaneously for controlling the operation of the hard disk 13. Asdiscussed above, the programme schedule data is transmitted regularly sothat the receiver 3 will be updated substantially continuously. Theinformation is brief to enable each channel to carry the programmeschedule data without excessive overheads in terms of bandwidthrequirements in each channel and memory requirements in the receiver.

In addition, a dedicated EPG channel transmits more detailed programmescheduling information. The information transmitted via this dedicatedchannel is updated more frequently and covers a longer period of time(e.g. one week). As a consequence, an up-to-date television programmeschedule of a complete week will always be available. As explained ingreater detail below, the receiver 3 is arranged to display theprogramme scheduling information on the TV 2. Also, a viewer caninteract with the receiver 3 to program recordings of televisionprogrammes, view a desired part of the available programme schedule,etc., on the basis of the information received via the dedicated EPGchannel.

Accordingly, while the programme schedule data in each channel is usedby the receiver 3 to operate the hard disk 13 to record a selectedtelevision programme in a selected channel at the correct up-to-datetime, the programme scheduling information in the dedicated EPG channelis used to display the programme schedule for several of the channelsover a predetermined period of time (which in turn is used forprogramming the receiver 3 as described below).

Since the tuners 10 a and 10 b can be tuned to receive differentchannels, it is possible for a first television programme in one channelto be displayed on a TV and recorded on the hard disk 13, while at thesame time a second television programme in another channel is alsorecorded on the hard disk 13.

The hard disk 13 of the receiver 3 is similar to conventional hard disksused in computer systems for storing large amounts of data. The harddisk 13 has a capacity of many gigabytes (e.g. 40 gigabytes) andreceives video and audio data for storage in the compressed form inwhich it is received, for example, in accordance with the DVB/MPEG 2standards as discussed above. This allows for the storage of severalhours of television programmes (e.g. 20+ hours) on the hard disk 13. Thehard disk 13 comprises two storage areas, one for the storage oftelevision programme data, and the other for storing “metadata” which isused to control the hard disk 13, as discussed in greater detail in ourearlier patent publications mentioned above. The processor 23 controlsthe operation of the hard disk 13. More-specifically, the processor 23controls the recording and playback of television programmes to and fromthe hard disk 13. Other processors (not shown) can be used to controlthe hard disk 13 as appropriate, but the control is described in thisdocument with reference to only processor 23 to facilitateunderstanding.

Referring to FIG. 2, a schematic block diagram of the arrangement of thehard disk 13 is shown. In this example, the hard disk 13 has three datachannels, through two of which data is received for storage on the harddisk 13 and through one of which data is output for subsequentdisplaying of television pictures. The three data channels consist oftwo data input channels 54 and 55 and one data output channel 56. Eachof the data channels has associated with it a data buffer 57, 58 and 59,respectively. Each of the data buffers 57, 58 and 59 comprises a RAM ofsufficient size to store several seconds of data (e.g. 8 megabytes). Theoperation of the data buffers 57, 58 and 59, as well as that of the harddisk 13, is controlled by the processor 23.

The hard disk 13 is operable to manage simultaneous reception of datathrough the data channels 54 and 55 and output of data through the datachannel 56. Data received through the data channels 54 and 55 is notstored directly on the hard disk 13 as it is received but is buffered bythe buffers 57 and 58, respectively. Likewise, data to be output throughthe data channel 56 is not output directly as it is read from the harddisk 13 but is buffered in the buffer 59.

The hard disk 13 is capable of managing a data rate that is higher thanthe rate at which data can be transferred through at least two of thethree channels 54, 55 and 56. Indeed, in this example, the hard disk 13is capable of managing a data rate at least as high as the rate of datatransmitted through all three channels 54, 55 and 56 combined.

The hard disk 13 is therefore capable of simultaneously storing datareceived through both the input channels 54 and 55 and outputting datathrough the output channel 56. This is achieved by buffering thereceived data and the data to be output in the buffers 57, 58 and 59,and by switching between them in order to transfer data from the inputbuffers 57 and 58 to the hard disk 13, or to transfer data from the harddisk 13 to the buffer 59.

Although hard disks comprising separate heads for writing and readingare available, in the interest of cost, in this example, the hard disk13 comprises one single head for both writing onto and reading from thehard disk 13. Therefore, while the hard disk 13 at any point in timestores/reads data associated with only one of the three data channels54, 55 and 56, it sequentially stores/reads data associated with thethree channels 54, 55 and 56, thereby “virtually” dealing with the threedata channels 54, 55 and 56 simultaneously.

The switching is controlled by the processor 23 by arbitrating betweenany three of the buffers 57, 58 and 59 at a frequency which is inaccordance with their buffer size so as to prevent a data overflow andthereby data loss. For example, if the buffers 57, 58 and 59 are capableof storing 8 megabytes of received data each, and the receiver 3 isoperated to record two simultaneous television programmes receivedthrough the channels 54 and 55 at an average data rate of approximately2 megabytes per second, then the hard disk 13 is operated to receivealternately data from the buffers 57 and 58 at an alternation cycle of 4seconds or preferably less, transferring the buffer content to the harddisk 13 each time the processor switches from one of the buffers 57, 58to the other. Accordingly, it is possible to recordsimultaneous/overlapping television programmes received by the first andsecond tuners 10 a, 10 b in different channels.

The buffering of incoming as well as outgoing data by the data buffers57, 58 and 59 means that the hard disk 13 does not need to besynchronised to a particular input or output data rate. Instead, thehard disk 13 always reads and stores data at the same constant datarate. The amount of data stored on or read from the hard disk 13 isdetermined by the duration for which the hard disk 13 is switched fordata transfer to the respective one of the data buffers 57, 58 or 59.During such time data is transferred from or to the respective databuffer 57, 58 or 59 at the constant data rate. While the reception datarate through the channels 54 and 55 or the output data rate through thechannel 56 may vary (for example depending on the bandwidth of receivedtelevision signals, or depending on the playback mode), the intermittentrate of data transfer between any of the buffers 57, 58 and 59 and thehard disk 13 is constant and determined by the data rate at which thehard disk 13 works.

The hard disk 13 is substantially the same as a hard disk from aconventional personal computer. As for computer data file systems, datais stored on the hard disk 13 in sectors, which might each store say 512kilobytes of data and may or may not be contiguous on the hard disk 13.The processor 23 uses file system software to manage the storing of dataon the hard disk 13 such that, regardless of how data is actually storedon the hard disk 13, it appears to be input and output as contiguousstream of data. More specifically, the processor 23 maintains a fileallocation table. When data is to be written on the hard disk 13, theprocessor 23 allocates sectors of the hard disk 13 to a new file. Thefile allocation table effectively links sectors of the hard disk 13together to form individual files as necessary, despite the individualsectors not neccessarily being contiguous.

A time counter 23 a for maintaining a record of the playback duration ofthe programme data recorded on the hard disk 13 is associated with theprocessor 23. The counter 23 a is shown as a separate unit from theprocessor 23 to facilitate understanding. It will however be appreciatedfrom the following that the counting function of the counter 23 a may inpractice be performed by registers within, or software running on, theprocessor 23.

In this example, there is a close correlation between the relativetiming of different portions of the data received at the receiver 3 (thearrival time) and the relative timing of the portions when they areintended to be displayed (the presentation time). This correlationexists despite the fact that the rate at which data is transmitted (i.e.the amount of data transmitted during a period), and therefore received,varies depending on content because, regardless of content, it takesapproximately one second to broadcast data for one second of aprogramme. The processor 23 and the counter 23 a take advantage of thisto ‘count’ time in the incoming programme data. In this example, thecounter does not simply count time from the beginning of programme datato be stored in a file as this can be complex if old data at thebeginning of the file is deleted. Instead, the counter counts anabsolute time (GMT or UTC for example). The count data is appended tothe programme data as it is written to the disk 13 in this example. Inanother example, the count data is written to a separate index registerfile on the disk 13, for example in the metadata area of the disk 13mentioned above.

As programme data is received by the receiver 3, it can be written to afile on the hard disk 13. More specifically, the received programme datacan be stored on the hard disk 13 as a linear file or in a so-called“review buffer”. A linear file has a defined start and programme data isadded to the file from the start until a defined end is reached. Incontrast, the review buffer has a defined start, but once the filecontains programme data of a specified duration, the processor 23deletes the beginning of the file and continues to record receivedprogramme data in the file in new sectors of the hard disk 13. (Inpractice, the new sectors might include some or all of those sectorsthat contained the data deleted from the beginning of the file, but onlyif the processor happens to allocate those new sectors to the file. Thisis not the same as simply overwriting sectors already permanentlyallocated to the file.)

The count data is most useful for the review buffer. For example, theprocessor 23 can monitor the count data for the programme data as it iswritten to a file on the hard disk 13. When the processor determinesthat the programme data in the file has a specified duration, theprocessor 23 can delete the beginning of the file whilst new programmedata is written at the end of the file such that the programme datastored in the file does not exceed the specified duration. Morespecifically, the processor 23 can move the start of the file. Forexample, the processor 23 can identify the sector in which the filestarts and then locate a subsequent sector of the file from the fileallocation table to which to move the start of the file, such that thesectors preceding the new start of the file are deleted from the file.

The count data can be used to control movement of the start of the file,i.e. to locate the subsequent sector to which to move the start of thefile. When the count data is appended to the programme data as it iswritten to the data file, the processor 23 reads the count data from thefile. When the count data indicates that (say) 30 seconds of programmedata has elapsed from the start of the file, the start of the file ismoved to the sector storing data including that point in the file. Whenthe counter 23 a and processor 23 subsequently indicate that (say) 30seconds of new programme data has been written at the end of the file,the start of the file is then moved again and so on. If the count datais stored in the separate index register, the processor 23 operates inthe same manner, except that data in the index register is read toidentify a point in the file at which (say) 30 seconds of the programmehas elapsed. In one example, the index register may store the number ofbytes of data periodically received and the new start of the file can beidentified by summing the number of bytes for the desired period (e.g.30 seconds).

This method of storing data provides the receiver 3 with greaterflexibility than has previously been possible. In particular, thereceiver 3 can change from recording just the last 30 minutes (say) ofthe programme in a review buffer, to recording the programme in itsentirety in a linear file straightforwardly, as long as the viewerselects ‘record’ for the programme within 30 minutes (say) from thestart of the programme. This is achieved by stopping moving the start ofthe review buffer. As soon as this is done, the review buffer iseffectively converted to a linear file. A new review buffer can then bestraightforwardly created by starting a new file if desired.

FIG. 3 of the accompanying drawings illustrates one way in which thehard disk 13 is controlled to store data during the recording of aprogramme. The hard disk 13 is arranged to record by default theprogramme currently being viewed by the viewer in a file on the harddisk 13. This file is referred to as a “review buffer” as mentionedabove. Under this default condition, which is depicted by time line A inFIG. 3, the hard disk 13 will store up to 30 minutes (say) of thecurrent programme. Typically, this length of time is preset as a defaulttime of 30 minutes during manufacture or configuration of the receiver3, but it may be user selected to be 0 minutes (i.e. turned off), 5minutes, 15 minutes, 30 minutes or 1 hour for example. Generally, anyperiod up to an hour could be chosen by a user. The recording beginswhen the user switches on the receiver 3 or when he switches to a newchannel. Recording continues until the designated period of time hasbeen recorded and thereafter continues with the oldest or earliest partsof the recording being deleted such that only the selected length of theprogramme is retained. This default recording operation is a backgroundoperation and requires no user interaction. Time line B showsprogression of the recording shown in time line A during the broadcastof a programme. In time line B, the length of the current programmestored in the review buffer is at it's maximum and does not include allof the programme from the time when the user switched on the receiver 3or switched channels. The same time line is also shown as time line C ofFIG. 3 at a later time when the review buffer includes the end of theprevious current programme and the beginning of a succeeding programme,i.e. extends on both sides of a programme start.

In the event that the user presses a “pause” button on the receiver 3 orthe remote control unit 28 during normal viewing of a broadcastprogramme, the receiver 3 enters a “live pause” mode. In this mode apaused frame of video is displayed on the TV 2, but the programmecontinues to be recorded. More specifically, if, as shown in time lineC, the review buffer includes the start of a programme when the livepause mode is entered, the content of the review buffer is truncated tothe start time of the current programme as shown in time line D. Inother words, all data stored in the review buffer that is older than thestart of the current programme is deleted. If the start time is notincluded in the review buffer when the live pause mode is entered, theentire programme recorded so far, i.e. all the data in the reviewbuffer, is retained. Thereafter, as shown in time line D, recordingcontinues with all data being held in the file. More specifically, thereview buffer is converted to a linear file by the deletion of data fromthe file being suspended. At the programme boundary, e.g. when the startof the next programme is received, the recordal of data in the linearfile is stopped and the next programme starts to be recorded in a newreview buffer, as shown in time lines D, E and F. The linear filetherefore includes the recorded programme, either in its entirety, orfrom the (say) 30 minutes (or whatever period is set by the user) frombefore the instant when the pause button was pressed until the end ofthe programme. The new review buffer contains the succeeding programmefrom the start.

In time line D, the viewer has commenced navigation within the recordedfile by pressing the “play” button or the “fast forward” button onremote control 28 and the receiver 3 is displaying the programme storedin the linear file. At the point shown in time line E, the receiver 3has reached the end of the programme stored in the linear file. In themeantime, the new review buffer has recorded the next succeedingprogramme for the default or selected period of time and is continuingto record the programme by deleting the earliest part of the recordedprogramme from the buffer. As the viewer cannot therefore view the startof the next succeeding programme (as it has already been deleted fromthe new review buffer), the receiver 3 returns the viewed to normalviewing by displaying the live broadcast as illustrated in time line F.The receiver is therefore effectively in the same state as in time lineB, but with the viewer watching, and the review buffer recording, alater broadcast programme.

Time lines A, B and C of FIG. 4 are identical to time lines A, B and Cof FIG. 3. Time line D of FIG. 4 illustrates recordal of the currentprogramme in live pause mode before the next succeeding programme startsto be recorded in a new review buffer. In time line E of FIG. 4, theviewer has pressed the “fast forward” button on the remote control 28and the receiver 3 is displaying the programme recorded in the linearfile at an increased rate. In time line F of FIG. 4, the receiver 3 hasdisplayed all of the programme recorded in the linear file and, in thisexample, is displaying the next succeeding programme as recorded in thenew review buffer. As can be seen from time lines E and F, the newreview buffer has not reached its maximum capacity and still containsthe start of the next programme when all of the programme stored in thelinear file has been displayed. The receiver 3 can therefore seamlesslycatch up with the live broadcast by displaying the contents of thelinear file and the new review buffer at an increased rate. In anotherexample, even when the review buffer includes the start of the nextprogramme, the viewer is returned to, i.e. the receiver 3 displays, thelive broadcast. Typically, the user is given a choice between these twoexamples, e.g. by display of an appropriate message.

In the above example, the live pause mode causes the entire reviewbuffer (subject to truncation) to be retained (as linear file) until therecorded programme has been viewed to the end. Thus, the viewer canrewind to beginning of the programme or to the length of the reviewbuffer before live pause mode was entered at any time until entireprogramme has been viewed. In another example, as soon as the viewerstarts to view the recorded programme, e.g. by pressing the “play” or“fast forward” buttons on the remote control 28, deletion of the startof the file recommences. More specifically, programme data before thedefault time of (say) 30 minutes or the selected time mentioned abovefrom the point in the recorded programme being viewed is deleted fromthe file. (In the event that the selected time is 0 minutes, programmedata before 5 minutes from the point in the recorded programme beingviewed is deleted from the file.) Memory space is therefore made freelyavailable more quickly than in the previous example.

Time lines A and B of FIG. 5 are the same as time lines A and B of FIG.3. However, in time line C of FIG. 5, the viewer presses a save buttonon the remote control 28 instead of the pause button as in time line Cof FIG. 3. Whilst the receiver therefore truncates the review buffer tothe start of the programme being recorded in the review buffer andconverts the review buffer to a linear file as in time line D of FIG. 3,in time lines D and E of FIG. 5, the receiver 3 saves the linear file.In particular, the title of the recorded programme is added to theuser's personal planner. The saving is actually carried out at the endof the recorded programme. In addition, if the user changes channelafter pressing the save button, the receiver continues to record theprogramme and the programme received in the new channel is recorded in anew review buffer.

Time lines A to D of FIG. 6 are the same as time lines A to D of FIG. 3.However, in time line E, whilst the viewer is fast forwarding throughthe stored programme, the viewer decides to save the programme andpresses the save key on the remote control 28. The receiver 3 thereforesaves the linear file at the end of the programme by adding theprogramme name to the viewer's personal planner and returns the viewerto the live broadcast in a similar manner to time lines E and F of FIG.3.

The receiver 3 is able to record one programme, while another programmeis being both viewed and recorded. The receiver also automaticallyrecords programmes in a review buffer or in a linear file withoutspecific input from a user. This greater flexibility and automation inrecording brings with it the possibility of conflict between demands formemory space of the hard disk 13. For example, allowing two programmesto be recorded simultaneously increases the likelihood of a conflictoccurring between programmes selected to be recorded and programmesalready recorded. In order to deal with this problem, the receiver 13includes a priority table, that may be user defined, but is normallydefined on configuration of the receiver 13.

One way in which existing recordings can be prioritised is to allow theviewer to select recordings that should never be automatically deleted(“keep events”) and to make decisions based on that selection. Keepevents take priority over any other recording and, if the hard disk isalready full of keep events, other recordings including automaticrecordings in the review buffer are abandoned in order to preserve thekeep events. The next highest priority is given to pay-per-view (PPV)programmes. These programmes are paid for and the viewer would thereforebe unhappy if a PPV recording was erased before being viewed. Next isother recorded but not yet viewed programmes, followed by recordingsalready viewed and recordings made while a programme was being viewed(e.g. the review buffer). Part-recorded programmes have lower prioritythan full recordings. Thus, if there is a disk space conflict, the firstrecordings to be deleted are the recordings made while a programme wasbeing viewed followed by recordings that have already been viewed, thenother recorded programmes and so on up to PPV programmes. Keep eventsare not usually automatically deleted.

Conflicts can also occur between programmes identified for recording.These conflicts can be dealt with in a similar manner by prioritisingthe programmes to be recorded. In this example, the highest priority isgiven to keep events, then PPV programmes, then scheduled programmesthat are series linked (e.g. an ongoing soap opera or series) and thenother scheduled programmes. The review buffer has lowest priority sinceit is a record of what the viewer has just seen. If two programmes wereto fall into the same priority group or category then the shorterprogramme is recorded in favour of the longer programme in the absenceof any other input from the viewer.

The receiver 3 may include the facility for extra-time recording inwhich a recording begins early or ends late in order to accommodateslight slippage in the broadcasting schedule. This extra time recordingcan cause conflicts with a start time for one programme being earlierthan a finish time for another programme. In this example, this conflictis dealt with by providing the end of one programme with priority overthe start of another and by giving a real end time priority over anextended end time.

This automatic prioritising of recordings need only be applied in theabsence of further input from the viewer. Conflicts can develop afterthe receiver 3 has been programmed because of a slip or other change inthe scheduled broadcast time of thee programme. In the event that aconflict develops, the receiver 3 is arranged to display a warning whenthe viewer turns on the receiver 3, inviting the viewer to adjust theprogrammed recordings. If the viewer does not turn on the receiver 3before the conflicting programmes are broadcast, then the prioritisingrules will be applied. Conflicts can, of course, also occur when theviewer is programming the receiver 3 to record programmes.

In either case, the receiver 3 will output display screens identifyingthe conflict and suggesting changes to the programmed recording in orderto resolve the conflict. The suggested changes are made based on thedefined priority rules. An example of a warning display screen is shownin FIG. 7 of the drawings. Here the viewer is watching channel 310 SkyPremier and the receiver is programmed to record both Enemy of the Stateand Shark Files. There are only two tuners 10 a, 10 b and so one of therecordings will have to be sacrificed if the viewer is to continuewatching channel 310 Sky Premier. The viewer can interact with thedisplay screen to cancel the recording of either Enemy of the State orShark Files, or can leave the programming as is, to end his viewing ofchannel 310 Sky Premier.

An example of a recording clash warning screen is shown in FIG. 8 of thedrawings. Here the viewer has previously programmed the receiver torecord Enemy of the State and Shark Files at times that overlap. Theviewer has then attempted to record The X Files at a time that conflictswith the broadcast (and recording) time of the other two programmes. Amessage, similar to that displayed on the screen of FIG. 7, is displayedadvising the viewer on how to resolve the conflict.

Another example of a recording clash warning screen is shown in FIG. 9of the drawings. Here the receiver 3 has been programmed to recordSimpsons and Charmed through one receiver 10 a and The Matrix andWeakest Link through the other receiver 10 b. Simpsons and The Matrixboth end at 7.30 pm, and Charmed and Weakest Link both start at 7.30 pm.When Heartbeat is added to the recording schedule a conflict occurs. Thereceiver 3 generates the display screen as shown, identifying theconflict with a highlight 300 and suggesting changes by highlighting aprogramme 302 (in this case Simpsons) that should be deleted. Viewerinteraction will result in the screen being changed to that shown inFIG. 10, in which programme 302 is no longer shown and programme 304(Weakest Link) is highlighted as the suggested deletion. Furtherinteraction will result in the screen shown in FIG. 11 being displayed,in which Heartbeat is programmed to be recorded via one receiver 10 a,and The Matrix and Charmed are programmed to be recorded via the otherreceiver 10 b. Other screens are of course possible depending on thenumber of tuners 10 a, 10 b, the priority rules and other features ofthe system.

Modifications and variations such as will occur to those possessed ofappropriate knowledge and skills may be made to the above exampleswithout departure from the spirit and scope of the invention as set outin the appended claims and equivalents thereof.

1. A method of storing data comprising: receiving data at a variabledata rate that represents an information stream; storing the receiveddata; determining the expected duration of the information streamrepresented by the stored data should the information stream bereproduced as intended; and deleting the oldest stored data when thedetermined duration reaches a given period such that the determinedduration does not exceed the given period.
 2. The method of claim 1,wherein the information stream is intended to be reproduced at asubstantially constant rate.
 3. The method of claim 1, wherein the datarepresents a video stream.
 4. The method of claim 1, wherein theexpected duration of the information stream represented by the storeddata is determined as the period during which the stored data wasreceived.
 5. The method of claim 1, wherein the given period is adefault period that may be varied by a user.
 6. The method of claim 1,wherein: receiving the data comprises receiving a data stream ofcompressed video data delivered at a variable data rate; thedetermination comprises generating time information based on the time ofreceipt of the data and relating to the duration of the data when outputin decompressed form at a substantially constant data rate; storing thedata comprises writing the received data to a file in a store inreceived order together with the time information; and the deletioncomprises monitoring the time information of data written to the fileand deleting data from the file when the total amount of data in thefile corresponds to a period of time greater than a predetermined periodso that at any instant in time the amount of data in the file is of aduration no greater than the predetermined period.
 7. The method of anyone of claims 1, wherein the data is stored as a data file in a memoryand the oldest stored data is deleted by moving the start of the datafile to data representing information later in the information stream.8. A method of storing data, comprising storing a data stream as a datafile in a memory such that the data file does not exceed a specifiedsize by deleting the oldest stored data from the data file whilststoring new data at the end of the data file, wherein the oldest data isdeleted by moving the start of the data file to later in the stored datastream.
 9. The method of claim 7, wherein the memory is formatted asplural storage sectors and the data file occupies a series of thestorage sectors.
 10. The method of claim 9, wherein the start of thedata file is identified as at a particular storage sector.
 11. Themethod of claim 10, wherein the start of the file is moved byidentifying another particular storage sector later in the series ofstorage sectors such that the preceding storage sectors in the seriesare removed from the data file.
 12. A method of recording datarepresenting a programme for subsequent playback of the programme, themethod comprising: storing one set of received data for one programme ina store while simultaneously outputting the same data for display of theprogramme represented thereby, the one set of received data being storedin accordance with the method of claim 1; and simultaneously recordinganother set of received data for another programme in the store.
 13. Amethod of recording television programmes, the method comprising storingtimes that programmes are to be recorded and revising the stored timesif there is a overlap in the time that two or more programmes are to berecorded to give priority to the programme having programme type withhigher priority on a stored programme type priority list.
 14. The methodof claim 13, comprising revising the stored times if there is a overlapin the time that two or more programmes are to be recorded to givepriority in turn to programmes having respective programme types withhigher respective priorities on a stored programme type priority list15. A method of making recordings of plural programmes, the methodcomprising: generating a priority list identifying types of programmesto be recorded and their relative priorities; storing timing informationrelating to one or more programmes to be recorded together withinformation identifying the type of programme to be recorded; comparingentries on the priority list with the stored timing and type informationfor each programme to be recorded; and revising the stored timinginformation in the event of a conflict between timing information fortwo or more programmes to be recorded, depending on the relativepriorities of the conflicting programmes.
 16. A method of controlling arecorder to record programmes, the method comprising: storing a prioritylist identifying types of programmes to be recorded and their relativepriorities; storing timing information relating to one or moreprogrammes to be recorded together with information identifying the typeof programme to be recorded; receiving a data stream including datarepresenting programme content, programme identity data and dataidentifying the broadcast times of programmes; comparing the storedtiming information with the received data identifying the broadcasttimes of programmes; adjusting the stored timing information in theevent of a change as determined from the received data identifying thebroadcast times of programmes; comparing entries on the priority listwith the stored timing and type information for each programme to berecorded; and revising the stored timing information in the event of aconflict between timing information for two or more programmes to berecorded, depending on the relative priorities of the conflictingprogrammes.
 17. An apparatus for storing data comprising: a receiver forreceiving data at a variable data rate that represents and informationstream; a storage device for storing the data; and a processor fordetermining the expected duration of the information stream representedby the stored data should the information stream be reproduced asintended; wherein the storage device deletes the oldest stored data whenthe determined duration reaches a given period such that the determinedduration does not exceed the given period.
 18. The apparatus of claim17, wherein the information stream is intended to be reproduced at asubstantially constant rate.
 19. The apparatus of claim 17, wherein thedata represents a video stream.
 20. The apparatus of claim 17, whereinthe processor determines the expected duration of the information streamrepresented by the stored data as the period during which the storeddata was received.
 21. The apparatus of claim 17, wherein the givenperiod is a default period and the apparatus comprises means by which auser can vary the default period.
 22. The apparatus of claim 17, whereinthe storage device is a hard disk.
 23. The apparatus of claim 17,wherein: the receiver comprises means for receiving a data stream ofcompressed video data delivered at a variable data rate; the processorcomprises means for generating time information based on the time ofreceipt of the data and relating to the duration of the data when outputin decompressed form at a substantially constant data rate; the storagedevice comprises means for writing the received data to a file in astore in received order together with the time information; and theprocessor further comprises means for monitoring the time information ofdata written to the file and means for deleting data from the file fromthe file when the total amount of data in the file corresponds to aperiod of time greater than a predetermined period so that at anyinstant in time the amount of data in the file is of a duration nogreater than the predetermined period.
 24. The apparatus of claim 17,wherein the storage device stores the data as a data file in a memoryand deletes the oldest stored data by moving the start of the data fileto data representing information later in the information stream.
 25. Anapparatus for storing data, comprising means for storing a data streamas a data file in a memory and a file manager for managing the size ofthe data file such that it does not exceed a specified size by deletingthe oldest data stored in the data file whilst new data is stored at theend of the data file, wherein the file manager deletes the old data bymoving the start of the data file to later in the stored data stream.26. The apparatus of claim 24, wherein the memory is formatted as pluralstorage sectors and the data file occupies a series of the storagesectors.
 27. The apparatus of claim 26, wherein the file manageridentifies the start of the data file as at a particular storage sector.28. The apparatus of claim 27, wherein the file manager moves the startof the file by identifying another particular storage sector later inthe series of storage sectors such that the preceding storage sectors inthe series are removed from the data file.
 29. An apparatus forrecording data representing a programme for subsequent playback of theprogramme, the apparatus comprising: means for storing one set ofreceived data for one programme in a store while simultaneouslyoutputting the same data for display of the programme representedthereby, the one set of received data being stored by the apparatus ofclaim 17; and means for recording another set of received data foranother programme in the store.
 30. An apparatus for recordingtelevision programmes, the apparatus comprising means for storing timesthat programmes are to be recorded and means for revising the storedtimes if there is a overlap in the time that two or more programmes areto be recorded to give priority to the programme having programme typewith higher priority on a stored programme type priority list.
 31. Theapparatus of claim 30, wherein the revising means revises the storedtimes if there is a overlap in the time that two or more programmes areto be recorded to give priority in turn to programmes having respectiveprogramme types with higher respective priorities on a stored programmetype priority list
 32. An apparatus for making recordings of pluralprogrammes, the apparatus comprising: means for generating a prioritylist identifying types of programmes to be recorded and their relativepriorities; means for storing timing information relating to one or moreprogrammes to be recorded together with information identifying the typeof programme to be recorded; means for comparing entries on the prioritylist with the stored timing and type information for each programme tobe recorded; and means for revising the stored timing information in theevent of a conflict between timing information for two or moreprogrammes to be recorded, depending on the relative priorities of theconflicting programmes.
 33. An apparatus for controlling a recorder torecord programmes, the apparatus comprising: means for storing apriority list identifying types of programmes to be recorded and theirrelative priorities; means for storing timing information relating toone or more programmes to be recorded together with informationidentifying the type of programme to be recorded; means for receiving adata stream including data representing programme content, programmeidentity data and data identifying the broadcast times of programmes;means for comparing the stored timing information with the received dataidentifying the broadcast times of programmes; means for adjusting thestored timing information in the event of a change as determined fromthe received data identifying the broadcast times of programmes; meansfor comparing entries on the priority list with the stored timing andtype information for each programme to be recorded; and means forrevising the stored timing information in the event of a conflictbetween timing information for two or more programmes to be recorded,depending on the relative priorities of the conflicting programmes. 34.A method of recording television programmes comprising: buffering atelevision signal currently being displayed on a television screen; andresponding to a request to record a television programme included in thetelevision signal by saving the buffered television signal along withsubsequent television signals to record the programme
 35. The method ofclaim 34, wherein the request to record the television programmecomprises pausing display of the television programme.
 36. The method ofclaim 34, wherein the request to record the television programmecomprises display of the buffered television signal.
 37. The method ofclaim 34, wherein the saved buffered television signal is truncated tothe start of the television programme.
 38. A method of displaying arecorded television programme comprising progressively deleting datarepresenting the recorded programme at a given interval behind theprogramme as it is displayed.
 39. An apparatus for recording televisionprogrammes comprising: a memory for buffering a television signalcurrently being displayed on a television screen; and a processor forresponding to a request to record a television programme included in thetelevision signal by saving the buffered television signal along withsubsequent television signals to record the programme
 40. The apparatusof claim 39, wherein the request to record the television programmecomprises pausing display of the television programme.
 41. The apparatusof claim 39, wherein the request to record the television programmecomprises display of the buffered television signal.
 42. The apparatusof claim 39, wherein the processor truncates the saved bufferedtelevision signal to the start of the television programme.
 43. Anapparatus for displaying a recorded television programme comprising aprocessor progressively deleting data representing the recordedprogramme at a given interval behind the programme as it is displayed.44. A television signal receiver including the apparatus of claim 17.45. (canceled)
 46. The method of claim 8, wherein the memory isformatted as plural storage sectors and the data file occupies a seriesof the storage sectors.
 47. The method of claim 46, wherein the start ofthe data file is identified as at a particular storage sector.
 48. Themethod of claim 47, wherein the start of the file is moved byidentifying another particular storage sector later in the series ofstorage sectors such that the preceding storage sectors in the seriesare removed from the data file.
 49. The apparatus of claim 25, whereinthe memory is formatted as plural storage sectors and the data fileoccupies a series of the storage sectors.
 50. The apparatus of claim 49,wherein the file manager identifies the start of the data file as at aparticular storage sector.
 51. The apparatus of claim 50, wherein thefile manager moves the start of the file by identifying anotherparticular storage sector later in the series of storage sectors suchthat the preceding storage sectors in the series are removed from thedata file.